1. Field of the Invention
The present invention relates to high-frequency oscillators and electronic apparatus using the oscillators; for example, to an oscillator used as a local oscillator in a communication apparatus, and to other electronic apparatus using the oscillator.
2. Description of the Related Art
Conventional high-frequency oscillators have structures as disclosed, for example, in Unexamined Japanese Patent Application Publication No. Sho-63-9203 and Unexamined Japanese Patent Application Publication No. Hei-10-173439.
In Unexamined Japanese Patent Application Publication No. Sho-63-9203, an oscillator mainly including a dielectric substrate, a cylindrical dielectric resonator made from a large-dielectric-constant dielectric, a semiconductor device, and a metallic case is disclosed in an outlined manner. The dielectric resonator is mounted on the dielectric substrate through a support dielectric, is covered by the metallic case, resonates, for example, in TE01xcex4 mode, and is electromagnetically coupled with a microstrip line formed on the dielectric substrate. The microstrip line is connected to the semiconductor device mounted on the dielectric substrate. These components together form an oscillating circuit having a resonating circuit section and an amplifying circuit section.
In Unexamined Japanese Patent Application Publication No. Hei-10-173439, an oscillator mainly including a multi-layer substrate, a stripline resonator formed on an internal layer of the multi-layer substrate, and a semiconductor device mounted on a surface of the multi-layer substrate is disclosed in an outlined manner. The stripline resonator is connected to the semiconductor device. These components together form an oscillating circuit having a resonating circuit section and an amplifying circuit section.
In the oscillator disclosed in Unexamined Japanese Patent Application Publication No. Sho-63-9203, however, since the dielectric resonator is placed on the dielectric substrate, it is very difficult to reduce positional shifts between the dielectric resonator and the microstrip line formed on the dielectric substrate, and it is also very difficult to reduce deviations in the oscillating frequency. In addition, because the cylindrical dielectric resonator is mounted on the dielectric substrate, the oscillator is relatively tall. It is difficult to make the oscillator low or compact.
In the oscillator disclosed in Unexamined Japanese Patent Application Publication No. Hei-10-173439, since the resonator has a low Q, deviations in the oscillating frequency become large and the stability of the frequency deteriorates. In addition, because the stripline resonator is formed on an internal layer of the multi-layer substrate, the stripline resonator needs to have a dielectric layer (dielectric substrate) made from the same material as that used for the multi-layer substrate. It is very difficult to select the most appropriate material for the dielectric layer to obtain a resonator which has a stable frequency with respect to temperature changes.
The present invention solves the foregoing problems. Accordingly, an oscillator according to the present invention has a low profile, a small amount of deviation of the oscillating frequency, and high temperature stability; and an electronic apparatus using the oscillator has these advantages as well.
In one aspect of the present invention, the oscillator includes a dielectric substrate on which a microstrip-line resonator and a coupling line coupled with the microstrip-line resonator are formed; an active device is connected to the coupling line and constitutes an oscillating circuit together with the microstrip-line resonator; a package substrate, on which the dielectric substrate is mounted, has a smaller dielectric constant than the dielectric substrate; and the active device is mounted on the package substrate. In the oscillator, a frequency-variable device may be mounted on the package substrate.
In another aspect of the present invention, the oscillator includes a dielectric substrate on which a microstrip-line resonator and a coupling line coupled with the microstrip-line resonator are formed; an active device connected to the coupling line and constituting an oscillating circuit together with the microstrip-line resonator; and a package substrate on which the dielectric substrate is mounted and which has a smaller dielectric constant than the dielectric substrate, wherein the active device is mounted on the dielectric substrate. In the oscillator, a frequency-variable device may be mounted on the dielectric substrate.
In the oscillator, a bias line and a bias resistor both for applying a bias voltage to the active device may be formed on the dielectric substrate.
In the oscillator, for manufacturing efficiency, the microstrip-line resonator and the coupling line may be formed at the same time by the same electrode forming method. The electrode forming method may be a thin-film-electrode forming method, such as evaporation or sputtering, for example. The microstrip-line resonator and the coupling line may be formed by photolithography. The electrode forming method may be a thick-film-electrode forming method such as screen printing, for example.
Efficiency may also be achieved by making the resonator and coupling line by the same method but at different times; or at the same time but by different or similar methods.
In the oscillator, the dielectric substrate may be mounted on the package substrate by die bonding. The dielectric substrate and the package substrate may be electrically connected by wire bonding. The dielectric substrate may be mounted on the package substrate by flip-chip mounting.
The dielectric substrate may have a relative permittivity of 20 or more.
The temperature characteristic of the dielectric substrate may be specified such that the temperature drift of the resonant frequency of the microstrip-line resonator is within 0.1% of the resonant frequency in a temperature range of 0xc2x0 C. to 70xc2x0 C.
In the oscillator, the package substrate may be an alumina substrate. The package substrate may be a resin substrate.
The oscillator may further include an electrically conductive cap for sealing the dielectric substrate mounted on the package substrate, and the active device.
In still another aspect of the present invention, an electronic apparatus includes an oscillator as described above.
With the above structures, an oscillator according to the present invention is made to have a low profile. In addition, the oscillator has a narrow oscillating frequency deviation. Furthermore, the oscillator has high temperature stability. In addition, when the active device is mounted on the dielectric substrate, the oscillator is compact and has a low profile.
When a frequency-variable device is mounted on the package substrate or on the dielectric substrate, the oscillator can serve as a voltage-controlled oscillator.
When the microstrip-line resonator and the coupling line are formed at the same time and/or by an identical or similar electrode forming method, or material, the oscillating frequency of the oscillator has a narrow deviation.
When the relative permittivity of the dielectric substrate is set to 20 or more, the microstrip-line resonator is made compact.
When the temperature characteristic of the dielectric substrate is specified such that the temperature drift of the resonant frequency of the microstrip-line resonator is within 0.1% of the resonant frequency in a temperature range of 0xc2x0 C. to 70xc2x0 C., high temperature stability is obtained.
When an electrically conductive cap is provided for sealing the dielectric substrate and the active device mounted on the package substrate, frequency stability is maintained against external electromagnetic interference.
In an electronic apparatus of the present invention, since an oscillator according to the present invention is used, a low profile and high performance are provided and high temperature stability is obtained.
Other features and advantages of the invention will be understood from the following description of embodiments thereof, with reference to the drawings, in which like references denote like elements and parts.